This invention relates to hydrometallurgical leaching processes and apparatus and more particularly to the recovery of copper or other metal values from ores by such leaching. Although the procedures and apparatus to be disclosed herein are set forth with specific reference to the hydrometallurgical leaching of copper ores, these same procedures and apparatus will be found applicable to other similar types or ores. Accordingly, the specific discussion of copper ores herein should be taken as an illustration of the specific application of the invention to that case. But, the scope of the invention should be taken more broadly, limited only by the scope of the appended claims.
In general, hydrometallurgical metal recovery processes include preparation of the material, usually ore, dissolution of the values from the ore into solution, and subsequent recovery from solution by suitable procedures. The dissolution step is commonly carried out as a leaching operation; the most frequently used procedures being heap leaching, percolation leaching, or some form of agitation leaching. While leaching under pressure or by bacterial action are also known, they are generally not of interest in the present context.
In some circumstances, heap leaching finds use with low grade ore bodies having marginal economics but generally requires a long leaching cycle which may extend for months and a high consumption of leaching solvent. In percolation leaching in vats the ore is crushed to the size of approximately 5/8 inch top size, after which the ore is loaded into the vats and the leach solution percolated through the ore at a predetermined rate. In general, the ore in vat leaching remains in static condition, and problems arise in attempting to reach high leaching efficiency due to excessive fines which develop during breakdown of the ore and which either block proper flow of the leaching solution through the vat or cause channeling of the flow such that the solution fails to reach such a large portion of the ore that extraction of all of the values becomes difficult if not impossible. Thus, while vat leaching is reasonable in cost with respect to operation and capital outlay and does not contain undue grinding requirements, it nevertheless is not completely satisfactory due to poor recovery and long leaching times. In addition, the exhausted ore has to be mechanically removed from the vat usually with grab buckets, which results in a material handling problem each time the vat is unloaded and also results in mechanical damage to the vat and consequent high maintenance costs.
In addition to the foregoing, various types of agitation leaching have been used particularly for fine materials obtained either from separation from crushed ores used in vat leaching or by additional grinding. Agitation is carried out either using mechanical agitators where the energy of mixing is supplied by a rotary shaft coupled to an impeller or raker arm, or the so-called Pachuca agitator, in which the agitation is supplied by an air lift rising through a slurry pulp of the ore and leaching solution. In order for either of these agitation systems to work properly, the additional grinding must be carried out to between minus 10 to minus 48 mesh. Agitation leaching of this size material does provide for high metal recovery rates; however, the capital cost and cost of operation of such a combination may be high, and requires high preparation costs associated with ore grinding and separation. Furthermore, there is a size range between the coarse material used in vat leaching and the finely ground material used in agitation leaching for which no really satisfactory leaching system exists.
In view of the above limitations and disadvantages there is a need for an improved process and apparatus for hydrometallurgical leaching.